Big, heavy mast

>Howdy all.
>
>How strong is strong?
>
>I have had a 2 1/2" schedule 80, 21 foot long piece of pipe stored for years
>hoping someday to use it for a mast. I measures just under 3" OD and weighs
>166 lbs. Just standard schedule 80 galvanized pipe. A real beast. I
>figured on machining down a piece of stock to fit in the end and to fit in
>the tailtwister. Figured I would pin it in place to hold it all together.
>That is, pin it in the pipe not the rotator. I have a pair of the tb-4's
>and planned on using both in this application like I do the tb-3 with
>smaller stuff. Makes it real handy when working on rotator. I usually keep
>about 6-7 feet of the mast in the tower.
> Although I have hefted long masts over the top of a tower in the past, I
>think I will "build" this one into the tower from the beginning. Put two
>sections together with the pipe inside and do the 'ol Iwo Jima trick.
>Unless, of course, there is a better way to get it done with the Rohn 45.
>
>For clarity, I'm really not a blivet when it comes to this stuff. I hve a
>ton of practical applications experience with this kind of stuff and tend to
>be conservative in my approach to things. I just thougt this would be a
>good follow-on to the thread that is currently being 'spun'.
>
>Any comments on suitability as a mast, loading, installing, etc.
>
>73, Steve, NJ4F
Hi Steve,
You can calculate exactly how safe using this mast will be. To do it,
however, you absolutley must have certain pieces of critical data about the
mast and the loads distributed on it. I wrote the whole process down and
submitted it to the NCJ a number of years ago. It was published and
received very well by the "tower community". It was published a second time
in the NCJ's tenth aniversary (I think) issue a couple of years ago as one
of their best articles from the past. I was very flattered.
Anyway, the important thing is that you can do your own engineering
calculations on this mast with the information you will find in the NCJ
article. As I said in my article (which you should get a copy of), you MUST
know the "yield strength" of the mast material you plan to use. It is a
critical number used in the calculations. Unfortunately, this number is
generally NOT known for "pipe" since what we normally call "pipe" is used to
carry fluids from one place to another, like water pipe. Pipe is not
specified for use as a structural member such as an antenna tower mast.
"Tubing", on the other hand, IS generally specified as a structural member
and "yield stength" numbers are readily available for it if you are certain
of the alloy and fabricating process. How could you possibly know this
information about a piece of pipe or tubing that you don't buy new, unless
the person you bought it from got that info when he bought it and saved it
for you? Very unlikely.
Bottom line is that you should use tubes and not pipes for masts and only
tubes you know a lot about, such as its "yield strength". This probably
means only new tubing.
Here is another hint: You can generally tell whether a piece of material is
a tube or a pipe by its dimensions. Since pipes are designed to carry
fluids, they are generally measured by inside diameter. "One and a half
inch pipe", for example, has an inside diameter of 1.5 inches. "Two inch
tubing" has an outside diameter of 2 inches. So measure the material you
have and you can see if the inside diameter or ouside diameter is a nice
round number. Then you will know if you are dealing with tubing or pipe.
If it is pipe, my advice is to forget it and buy a new piece of tubing. If
it is tubing, your next step is to determine its alloy and fabrication
process, which you might be able to do with the help of a metalurgist, so
that you will know the "yield strength" of it. You will probably find that
process is too expensive and/or difficult in which case I recommend you
forget it and buy a new piece of tubing.
Hey, I know you don't want to toss out a perfectly good piece of pipe or
tubing and waste your hard-earned money on something you might already own.
I've just seen too many mast failures in my day due to people using
materials they weren't absolutely sure of. Believe me, it just isn't worth it.
Here is a company that sell first class mast materials and can tell you
everything you ever wanted to know about it. I have no financial interest
in this company. I just want you to get the best advice you can on this
critical part of your installation:
Productivity Resources
P.O. Box 813
Belleville, TX 77418
Phone: (409) 865-2727
FAX: (409) 865-9800
Good luck, Steve, and let us all know how it works out for you.
Stan w7ni@teleport.com